Three-dimensional printing

ABSTRACT

In an example of a method for three-dimensional (3D) printing, build material layers are patterned to form an intermediate structure. During patterning, a binding agent is selectively applied to define: a build material support structure and a patterned intermediate part. Also during patterning, i) the binding agent and a separate agent including a gas precursor or ii) a combined agent including a binder and the gas precursor are selectively applied to define a patterned breakable connection between at least a portion of the build material support structure and at least a portion patterned intermediate part. The intermediate structure is heated to a temperature that activates the gas precursor to create gas pockets in the patterned breakable connection.

BACKGROUND

Three-dimensional (3D) printing may be an additive printing process used to make three-dimensional solid parts from a digital model. 3D printing is often used in rapid product prototyping, mold generation, mold master generation, and short run manufacturing. Some 3D printing techniques are considered additive processes because they involve the application of successive layers of material. This is unlike traditional machining processes, which often rely upon the removal of material to create the final part. Some 3D printing methods use chemical binders or adhesives to bind build materials together. Other 3D printing methods involve at least partial curing, thermal merging/fusing, melting, sintering, etc. of the build material. For some materials, at least partial melting may be accomplished using heat-assisted extrusion, and for some other materials (e.g., polymerizable materials), curing or fusing may be accomplished using, for example, ultra-violet light or infrared light.

BRIEF DESCRIPTION OF THE DRAWINGS

Features of examples of the present disclosure will become apparent by reference to the following detailed description and drawings, in which like reference numerals correspond to similar, though perhaps not identical, components. For the sake of brevity, reference numerals or features having a previously described function may or may not be described in connection with other drawings in which they appear.

FIG. 1 is a flow diagram illustrating an example of a 3D printing method disclosed herein;

FIGS. 2A through 2D are schematic views of different examples of intermediate structures, each of which includes a build material support structure, a patterned intermediate part, and a patterned breakable connection defined between at least a portion of the build material support structure and the patterned intermediate part;

FIG. 3 is a flow diagram illustrating another example of the 3D printing method disclosed herein;

FIGS. 4A through 4J are schematic and partially cross-sectional views depicting the formation of a 3D object and a 3D support structure using an example of the 3D printing method disclosed herein; and

FIG. 5 is a simplified isometric and schematic view of an example of a 3D printing system disclosed herein.

DETAILED DESCRIPTION

In some examples of three-dimensional (3D) printing, a liquid functional agent is selectively applied to a layer of build material on a build platform to pattern a selected region of the layer, and then another layer of the build material is applied thereon. The liquid functional agent may be applied to this other layer of build material, and these processes may be repeated to form a green part (also known as a green body, and referred to herein as a patterned intermediate part) of the 3D part that is ultimately to be formed. The liquid functional agent is capable of penetrating the layer of build material onto which it is applied, and spreading onto the exterior surface of the build material particles of that layer. The liquid functional agent may include a binder that holds the build material particles of the patterned intermediate part together. The patterned intermediate part may then be exposed to heat to sinter the build material in the patterned intermediate part to form the 3D object/part.

In some 3D printing methods, sections of a patterned intermediate part may not directly be supported by the build platform during the patterning process, and/or may not be supported by a heating mechanism platform during the sintering process. A lack of support can lead to deformation of those sections during patterning and/or sintering. The lack of support may be undesirable because it may render the final finished part otherwise unusable, aesthetically unpleasing, etc. In the examples disclosed herein, a build material support structure is built as the patterned intermediate part is built, which provides support to the patterned intermediate part during patterning. Also in the examples disclosed herein, the build material support structure is temporarily bound to the patterned intermediate part and thus can be moved to a heating mechanism platform with the patterned intermediate part to provide support during sintering.

As mentioned herein, the build material support structure is temporarily bound to the patterned intermediate part at a patterned breakable connection. During sintering, the patterned breakable connection forms an irreversibly breakable connection that includes a plurality of gas pockets. These gas pockets provide the irreversibly breakable connection with fragility, which allows the 3D support structure to be easily removed from the 3D object.

Definitions

Throughout this disclosure, it is to be understood that terms used herein will take on their ordinary meaning in the relevant art unless specified otherwise. Several terms used herein and their meanings are set forth below.

The singular forms “a”, “an”, and “the” include plural referents unless the context clearly dictates otherwise.

The terms comprising, including, containing and various forms of these terms are synonymous with each other and are meant to be equally broad.

As used herein, the terms “remaining region of the patterned intermediate part,” “portion of the patterned intermediate part,” or “layer of the patterned intermediate part” refers to a subsection of the intermediate part that does not have a shape representative of the final 3D printed part, and that includes build material particles patterned with a binding liquid functional agent (i.e., binding agent). In the remaining portion, the portion, or the layer of the patterned intermediate part, the build material particles may or may not be weakly bound together by one or more components of the binding liquid functional agent and/or by attractive force(s) between the build material particles and the binding agent. Moreover, it is to be understood that any build material that is not patterned with the binding agent is not considered to be part of the portion of the patterned intermediate part, even if it is adjacent to or surrounds the portion of the patterned intermediate part.

As used herein, the term “patterned intermediate part” refers to an intermediate part that has a shape representative of the final 3D printed part, and that includes build material particles patterned with the binding agent. In the patterned intermediate part, the build material particles may or may not be weakly bound together by one or more components of the binding agent and/or by attractive force(s) between the build material particles and the binding agent. In some instances, the mechanical strength of the patterned intermediate part is such that it cannot be handled or extracted from a build platform. Moreover, it is to be understood that any build material that is not patterned with the binding liquid functional agent is not considered to be part of the patterned intermediate part, even if it is adjacent to or surrounds the patterned intermediate part.

As used herein, the term “build material support structure” refers to at least one layer of build material that is patterned with the binding agent and that provides support for i) an additional layer of build material that is patterned with the gas generating liquid functional agent, ii) additional layer(s) of build material that are patterned with the binding agent, and/or iii) patterned layers during sintering.

Also as used herein, a “patterned breakable connection” refers to a layer of build material patterned with the gas generating liquid functional agent and positioned between at least a portion of the build material support structure and at least a portion of the patterned intermediate part.

As used herein, the term “intermediate structure” includes the patterned intermediate part and the build material support structure temporarily bound together by the patterned breakable connection.

As used herein, the term “densified intermediate part” refers to a patterned intermediate part from which the liquid components of the binding agent have at least substantially evaporated. At least substantial evaporation of the liquid components of the binding agent leads to densification of the intermediate part, which may be due to capillary compaction. The at least substantial evaporation of the binding agent may also allow the binder to bind the build material particles of the densified intermediate part. In other words, the “densified intermediate part” is an intermediate part with a shape representative of the final 3D printed part and that includes the build material particles bound together by the binder. Compared to the patterned intermediate part, the mechanical strength of the densified intermediate part is greater, and the densified intermediate part can be handled or extracted from the build area platform.

The patterned or densified intermediate part may be known as a green part, but it is to be understood that the term “green” when referring to the patterned intermediate/green part or the densified intermediate/green part does not connote color, but rather indicates that the part is not yet fully processed.

As used herein, the term “at least substantially binder-free intermediate part” refers to an intermediate part that has been exposed to a heating process that initiates thermal decomposition of the binder so that the temporary binder is at least partially removed. In some instances, volatile organic components of, or produced by the thermally decomposed binder are completely removed and a very small amount of non-volatile residue from the thermally decomposed binders may remain. The small amount of the non-volatile residue is generally <2 wt % of the initial binder amount, and in some instances is <0.1 wt % of the initial binder amount. In other instances, the thermally decomposed binder (including any products and residues) is completely removed. In other words, the “at least substantially binder-free intermediate part” refers to an intermediate part with a shape representative of the final 3D printed part and that includes build material particles bound together as a result of i) weak sintering (i.e., low level necking between the particles, which is able to preserve the part shape), or ii) a small amount of the non-volatile binder residue remaining, and/or iii) a combination of i and ii.

The at least substantially binder-free intermediate part may have porosity similar to or greater than the densified intermediate part (due to temporary binder removal), but the porosity is at least substantially eliminated during the transition to the 3D printed part/object.

The at least substantially binder-free intermediate part may be known as a gray part, but it is to be understood that the term “gray” when referring to the at least substantially binder-free gray part does not connote color, but rather indicates that the part is not yet fully processed.

As used herein, the terms “3D printed part or object,” “3D part,” and “3D object” refer to a completed, sintered part.

As used herein, the “gas generating liquid functional agent” refers to a liquid functional agent that includes a compound that will decompose or react with an oxidizing agent during heating of the intermediate structure to generate gas pockets within a portion of the intermediate structure that is patterned with the gas generating liquid functional agent. “Gas pockets” are voids, spaces, or pores that are formed among build material and/or coalesced (e.g., sintered) build material as a reaction product of a reaction involving the compound during heating of the intermediate structure. In some examples, the gas generating liquid functional agent is a separate agent used in combination with the binding agent. In these examples, the gas generating liquid functional agent does not include a binder. In other examples, the gas generating liquid functional agent may also include the binder that can temporarily bind the build material of the patterned breakable connection. In these examples, the gas generating liquid functional agent may be referred to as a combined agent, and a separate binding agent may not be used for patterning the breakable connection. Examples of the gas generating liquid functional agent are described further herein below.

Also as used herein, the “binding liquid functional agent” or “binding agent” refers to a patterning fluid that includes a binder, but that does not include the compound that will decompose or react to form the gas pockets upon heating. Examples of the binding agent are described further herein below.

It is to be understood that the weight percentages provided herein may vary, depending upon the weight percentage of the active components within a solution, dispersion, etc. used to form the binding agent, gas generating liquid functional agent, etc., and also on the desired weight percentage of the active components within the binding agent, gas generating liquid functional agent, etc. For example, if a dispersion (to be added to the binding agent) includes 10% of the active component, and the target weight percentage of the active component in the binding agent is 0.01%, then the amount of the dispersion that is added is 0.1% to account for the non-active components in the dispersion.

The examples disclosed herein provide several methods for forming the intermediate structure, and the final sintered object, support, and connection. In some examples, both the gas generating liquid functional agent and the binding liquid functional agent are utilized in forming the patterned breakable connection. In other examples, the patterned breakable connection is formed using the combined agent. In the examples disclosed herein, the same types of build material, gas generating liquid functional agents, and/or binding liquid functional agents may be used. Each of the components will now be described.

Build Material

In examples of the method disclosed herein, the same build material may be used for generating the 3D part, the support structure, and the irreversibly breakable connection. The build material can include metal build material.

In an example, the build material particles are a single phase metallic material composed of one element. In this example, the sintering temperature may be below the melting point of the single element.

In another example, the build material particles are composed of two or more elements, which may be in the form of a single phase metallic alloy or a multiple phase metallic alloy. In these other examples, sintering generally occurs over a range of temperatures.

The build material particles may be composed of a single element or alloys. Some examples of the metallic build material particles include steels, stainless steel, bronzes, titanium (Ti) and alloys thereof, aluminum (Al) and alloys thereof, nickel (Ni) and alloys thereof, cobalt (Co) and alloys thereof, iron (Fe) and alloys thereof, nickel cobalt (NiCo) alloys, gold (Au) and alloys thereof, silver (Ag) and alloys thereof, platinum (Pt) and alloys thereof, and copper (Cu) and alloys thereof. Some specific examples include AlSi10Mg, 2xxx series aluminum, 4xxx series aluminum, CoCr MP1, CoCr SP2, MaragingSteel MS1, Hastelloy C, Hastelloy X, NickelAlloy HX, Inconel IN625, Inconel IN718, SS GP1, SS 17-4PH, SS 316L, SS 430L, Ti6Al4V, and Ti-6Al-4V ELI7. While several example alloys have been provided, it is to be understood that other alloys may be used.

The temperature(s) at which the metallic particles sinter is/are above the temperature of the environment in which the patterning portion of the 3D printing method is performed (e.g., above 100° C.). In some examples, the metallic build material particles may have a melting point ranging from about 500° C. to about 3500° C. In other examples, the metallic build material particles may be an alloy having a range of melting points.

The build material particles may be similarly sized particles or differently sized particles. The individual particle size of each of the build material particles is up to 100 μm. In an example, the build material particles may be particles, having a particle size ranging from about 1 μm to about 100 μm. In another example, the individual particle size of the build material particles ranges from about 1 μm to about 30 μm. In still another example, the individual particle size of the build material particles ranges from about 2 μm to about 50 μm. In yet another example, the individual particle size of the build material particles ranges from about 5 μm to about 15 μm. In yet another example, the individual particle size of the build material particles ranges from about 3.25 μm to about 5 μm. In yet another example, the individual particle size of the build material particles is about 10 μm. As used herein, the term “individual particle size” refers to the particle size of each individual build material particle. As such, when the build material particles have an individual particle size ranging from about 1 μm to about 100 μm, the particle size of each individual build material particle is within the disclosed range, although individual build material particles may have particle sizes that are different than the particle size of other individual build material particles. In other words, the particle size distribution may be within the given range. The particle size of the build material particles generally refers to the diameter or volume weighted average/mean diameter of the build material particle, which may vary, depending upon the morphology of the particle. The build material particles may also be non-spherical, spherical, random shapes, or combinations thereof.

Gas Generating Liquid Functional Agent

The gas generating liquid functional agent may be used to pattern build material where it is desirable to form the irreversibly breakable connection. Some examples of the gas generating liquid functional agent are used with a separate binding agent; and other examples of the gas generating liquid functional agent are a combined agent that includes the binder, and thus are not used with a separate binding agent.

Whether a separate agent or a combined agent, in some examples, the gas generating liquid functional agents disclosed herein are aqueous (i.e., water) based liquids including a gas precursor compound(s). In other examples, the gas generating liquid functional agents disclosed herein are solvent based liquids including the gas precursor compound(s).

The gas precursor includes a compound that is to be activated, at a temperature within a sintering temperature range of a build material of an intermediate structure, to generate gas pockets within a portion of the intermediate structure that is patterned with the gas generating liquid functional agent, the compound being selected from the group consisting of a transition metal hydride, an alkaline earth carbonate selected from the group consisting of barium carbonate and strontium carbonate, and a solid state mixture of an oxidizable species and an oxidizing agent to produce an oxidation product in a gas state in the sintering temperature range. As such, the gas precursor compound(s) is selected such that it undergoes reaction(s) to initiate gas formation at the high temperatures used in the sintering stage(s) of the printing process. This high activation temperature property, therefore, limits the type of gas precursor compounds that are capable of producing the mechanically weak junctions between the sintered object/part and the sintered support structure. In the examples disclosed herein, the gas precursor compound(s) may undergo thermal decomposition or oxidation when exposed to temperature(s) within a sintering temperature range of the printing process.

Some examples of the gas precursor compound(s) include inorganic materials that produce gas through thermal decomposition. Suitable inorganic materials include transition metal hydrides (for example, titanium hydride, TiH_((2-X))) and alkaline earth carbonates (for example, calcium carbonate, barium carbonate, strontium carbonate).

At temperatures between about 300° C. to about 500° C., titanium hydride decomposes slowly, releasing hydrogen. Given its non-stoichiometric nature, however, its rate of decomposition increases with further increase in temperature until the melting temperature of metallic titanium is reached. Thus, titanium hydride can be used as a gas precursor compound when it is desirable to form gas pockets at a temperature range of from about 500° C. to about 900° C. Titanium hydride may be a suitable gas precursor compound with an aluminum build material. Titanium hydride is hydrolytically stable, and thus can be readily incorporated into the aqueous based agents disclosed herein.

Alkaline earth carbonates decompose releasing carbon dioxide (CO₂) at elevated temperatures. In other words, the gas precursor is an alkaline earth carbonate that releases CO₂ when activated. Examples of the alkaline earth carbonates that may be suitable gas precursor compound(s) include calcium carbonate (which thermally decomposes at about 840° C.), barium carbonate (which thermally decomposes at about 1,360° C.), and strontium carbonate (which thermally decomposes at temperatures ranging from about 1,100° C. up to about 1,500° C.). In an example, the alkaline earth carbonate has a particle size less than 100 nm. A greater CO₂ concentration in the atmosphere during thermal decomposition can increase the carbonate decomposition temperature. As such, it may be desirable for alkaline earth carbonate decomposition to take place in an inert, reducing, or vacuum environment.

Some other examples of the gas precursor compound(s) include materials that produce gas through oxidation. Examples of these materials include solid state mixtures of oxidizable species with oxidizing agents. Components for the solid state mixtures are chosen such that i) the gas forming redox reactions in the mixtures are activated at the sintering temperatures of the metal part, and ii) the reducing and oxidizing components in the mixtures are present in stoichiometric ratio, thereby enabling a maximum yield of gas produced by the redox reaction. In examples of the solid state mixtures, the oxidizable species includes carbon particles and the oxidizing agent is a transition metal oxide selected from the group consisting of Fe₂O₃ (iron (III) oxide), Mn₂O₃ (manganese (III) oxide), Cr₂O₃ (chromium (III) oxide), Co₃O₄ (cobalt (II, III) oxide), etc. The gas produced from such oxides may include the carbon oxide gases, carbon dioxide (CO₂) and carbon monoxide (CO). The gas production from such oxides may proceed according to the scheme illustrated in equations I to IV below:

2Me₂O₃+3C→4Me+3CO₂  (I)

2Me₂O₃+3C→4Me+6CO  (II)

Me₃O₄+2C→3Me+2CO₂  (III)

Me₃O₄+4C→3Me+4CO  (IV)

where Me represents metal. When ferrous oxides are used in the reactions above, the reactions proceed with rates and yield at temperatures typically higher than about 900° C. to about 1000° C., which overlaps with the temperature range used for the sintering of ferrous alloy powders.

The gas precursor compound may be present in the gas generating liquid functional agent in an amount ranging from about 1 wt % to about 75 wt % of the total weight of the gas generating liquid functional agent. In another example, the gas precursor compound may be present in the gas generating liquid functional agent in an amount ranging from about 2 wt % to about 40 wt % or about 50 wt % of the total weight of the gas generating liquid functional agent. These percentages may include both active gas precursor compound and other non-active components present with the compound. It is to be understood that the upper limit may be increased as long as the gas generating liquid functional agent can be jetted via a desired inkjet printhead.

When the gas generating liquid functional agent is used with a separate binding agent, the gas generating liquid functional agent may include the previously described compound (i.e., gas precursor compound), any of a surfactant or a dispersing aid, a co-solvent, and a balance of water. The separate gas generating liquid functional agent may also include antimicrobial agent(s) and/or anti-kogation agent(s), but does not include a binder.

The co-solvent may be an organic co-solvent present in the gas generating liquid functional agent in an amount ranging from about 0.5 wt % to about 50 wt % (based on the total weight of the gas generating liquid functional agent). It is to be understood that other amounts outside of this range may also be used depending, at least in part, on the jetting architecture used to dispense the gas generating liquid functional agent. The organic co-solvent may be any water miscible, high-boiling point solvent, which has a boiling point of at least 120° C. Classes of organic co-solvents that may be used include aliphatic alcohols, aromatic alcohols, diols, glycol ethers, polyglycol ethers, 2-pyrrolidones/pyrrolidinones, caprolactams, formamides, acetamides, glycols, and long chain alcohols. Examples of these co-solvents include primary aliphatic alcohols, secondary aliphatic alcohols, 1,2-alcohols, 1,3-alcohols, 1,5-alcohols, ethylene glycol alkyl ethers, propylene glycol alkyl ethers, higher homologs (C₆-C₁₂) of polyethylene glycol alkyl ethers, N-alkyl caprolactams, unsubstituted caprolactams, both substituted and unsubstituted formamides, both substituted and unsubstituted acetamides, and the like. In some examples, the gas generating liquid functional agent may include 2-pyrrolidone, 1,2-butanediol, 2-methyl-1,3-propanediol, 1-(2-hydroxyethyl)-2-pyrrolidone, or combinations thereof.

The gas generating liquid functional agent may also include surfactant(s) and/or dispersing aid(s). Surfactant(s) and/or dispersing aid(s) may be used to improve the wetting properties and the jettability of the gas generating liquid functional agent. Examples of suitable surfactants and dispersing aids include those that are non-ionic, cationic, or anionic. Examples of suitable surfactants/wetting agents include a self-emulsifiable, non-ionic wetting agent based on acetylenic diol chemistry (e.g., SURFYNOL® SEF from Air Products and Chemicals, Inc.), a non-ionic fluorosurfactant (e.g., CAPSTONE® fluorosurfactants from DuPont, previously known as ZONYL FSO), and combinations thereof. In a specific example, the surfactant is a non-ionic, ethoxylated acetylenic diol (e.g., SURFYNOL® 465 from Air Products and Chemical Inc.). In other examples, the surfactant is an ethoxylated low-foam wetting agent (e.g., SURFYNOL® 440 or SURFYNOL® CT-111 from Air Products and Chemical Inc.) or an ethoxylated wetting agent and molecular defoamer (e.g., SURFYNOL® 420 from Air Products and Chemical Inc.). Still other suitable surfactants include non-ionic wetting agents and molecular defoamers (e.g., SURFYNOL® 104E from Air Products and Chemical Inc.) or secondary alcohol ethoxylates (commercially available as TERGITOL® TMN-6, TERGITOL® 15-S-7, TERGITOL® 15-S-9, etc. from The Dow Chemical Co.). In some examples, it may be desirable to utilize a surfactant having a hydrophilic-lipophilic balance (HLB) less than 10. Examples of suitable dispersing aid(s) include those of the SILQUEST™ series from Momentive, including SILQUEST™ A-1230. Whether a single surfactant or dispersing aid is used or a combination of surfactants and/or dispersing aids is used, the total amount of surfactant(s) and/or dispersing aid(s) in the gas generating liquid functional agent may range from about 0.1 wt % to about 6 wt % based on the total weight of the gas generating liquid functional agent.

The gas generating liquid functional agent may also include antimicrobial agent(s). Suitable antimicrobial agents include biocides and fungicides. Example antimicrobial agents may include the NUOSEPT® (Ashland Inc.), UCARCIDE™ or KORDEK™ or ROCIMA™ (Dow Chemical Co.), PROXEL® (Arch Chemicals) series, ACTICIDE® B20 and ACTICIDE® M20 and ACTICIDE® MBL (blends of 2-methyl-4-isothiazolin-3-one (MIT), 1,2-benzisothiazolin-3-one (BIT), and Bronopol) (Thor Chemicals), AXIDE™ (Planet Chemical), NIPACIDE™ (Clariant), blends of 5-chloro-2-methyl-4-isothiazolin-3-one (CIT or CMIT) and MIT under the tradename KATHON™ (Dow Chemical Co.), and combinations thereof. In an example, the gas generating liquid functional agent may include a total amount of antimicrobial agents that ranges from about 0.01 wt % to about 1 wt %. In an example, the antimicrobial agent is a biocide and is present in the gas generating liquid functional agent in an amount of about 0.1 wt % (based on the total weight of the gas generating liquid functional agent). These percentages may include both active antimicrobial agent and other non-active components present with the antimicrobial agent.

An anti-kogation agent may also be included in the gas generating liquid functional agent. Kogation refers to the deposit of dried solids on a heating element of a thermal inkjet printhead. Anti-kogation agent(s) is/are included to assist in preventing the buildup of kogation, and thus may be included when the gas generating liquid functional agent is to be dispensed using a thermal inkjet printhead. Examples of suitable anti-kogation agents include oleth-3-phosphate (commercially available as CRODAFOS™ O3A or CRODAFOS™ N-3 acid) or dextran 500k. Other suitable examples of the anti-kogation agents include CRODAFOS™ HCE (phosphate-ester from Croda Int.), CRODAFOS® N10 (oleth-10-phosphate from Croda Int.), or DISPERSOGEN® LFH (polymeric dispersing agent with aromatic anchoring groups, acid form, anionic, from Clariant), etc. The anti-kogation agent may be present in the gas generating liquid functional agent in an amount ranging from about 0.1 wt % to about 1 wt % of the total weight of the gas generating liquid functional agent.

In some examples, the balance of the gas generating liquid functional agent is water (e.g., deionized water). In these examples, the amount of water may vary depending upon the weight percent of the other gas generating liquid functional agent components. In other examples, the balance of the gas generating liquid functional agent is a solvent (e.g., any of the previously listed co-solvents).

An example formulation of the gas generating liquid functional agent that does not include a binder, and thus may be used in combination with a separate binding agent, is shown in Table 1. This example includes calcium carbonate as the gas precursor compound.

TABLE 1 Component Actives Target Formulation Type Specific Components (wt %) (wt %) (wt %) Co-solvent 1-(2-Hydroxyethyl)-2- 100.00 20.00 20.00 pyrrolidone (HE-2P) Surfactant/ Silquest ™ 100.00 5.00 5.00 Dispersing aid Momentive A-1230 Surfynol ® 465 100.00 0.40 0.40 Antimicrobial Acticide ® M20 10.00 0.01 0.10 (stock solution) Gas Precursor Calcium carbonate 32.00 20.00 62.50 Compound (CaCO₃) 50 nm- 100 nm dispersion Water Deionized Water — — Balance

As mentioned herein, other examples of the gas generating liquid functional agent are combined agents that may be used to pattern build material to form the patterned breakable connection without using a separate binding agent. In these other examples, the gas generating liquid functional agent (or combined agent) includes the binder, the gas precursor, water or a solvent, co-solvent(s), and surfactant(s) and/or dispersing aid(s), and in some instances, may also include antimicrobial agent(s) and/or anti-kogation agent(s). In these examples, any of the previously described gas precursors, co-solvent(s), surfactant(s) and/or dispersing aid(s), antimicrobial agent(s), and/or anti-kogation agent(s) may be used in any of the given amounts.

Examples of suitable binders include latexes (i.e., an aqueous dispersion of polymer particles), polyvinyl alcohol, polyvinylpyrrolidone, and combinations thereof.

Examples of polyvinyl alcohol include low weight average molecular weight polyvinyl alcohols (e.g., from about 13,000 to about 50,000), such as SELVOL™ PVOH 17 from Sekisui. Examples of polyvinylpyrrolidones include low weight average molecular weight polyvinylpyrrolidones (e.g., from about 15,000 to about 19,000), such as LUVITEC™ K 17 from BASF Corp.

The polymer particles of the latex may have several different morphologies. For example, the polymer particles may be individual spherical particles containing polymer compositions of hydrophilic (hard) component(s) and/or hydrophobic (soft) component(s) that may be interdispersed according to IPN (interpenetrating networks), although it is contemplated that the hydrophilic and hydrophobic components may be interdispersed in other ways. For another example, the polymer particles may be made of a hydrophobic core surrounded by a continuous or discontinuous hydrophilic shell. For another example, the polymer particle morphology may resemble a raspberry, in which a hydrophobic core is surrounded by several smaller hydrophilic particles that are attached to the core. For still another example, the polymer particles may include 2, 3, or 4 particles that are at least partially attached to one another.

The latex polymer particles may have a weight average molecular weight ranging from about 5,000 to about 500,000. As examples, the weight average molecular weight of the latex particles may range from about 100,000 to about 500,000, or from about 150,000 to about 300,000.

Latex particles may include a heteropolymer including a hydrophobic component that makes up from about 65% to about 99.9% (by weight) of the heteropolymer, and a hydrophilic component that makes up from about 0.1% to about 35% (by weight) of the heteropolymer, where the hydrophobic component may have a lower glass transition temperature than the hydrophilic component. In general, a lower content of the hydrophilic component is associated with easier use of the latex particles under typical ambient conditions. As used herein, typical ambient conditions include a temperature range from about 20° C. to about 25° C., an atmospheric pressure of about 100 kPa (kilopascals), and a relative humidity ranging from about 30% to about 90%. The glass transition temperature of the latex particles may range from about −20° C. to about 130° C., or in a specific example, from about 60° C. to about 105° C.

Examples of monomers that may be used to form the hydrophobic component include C₁ to C₈ alkyl acrylates or methacrylates, styrene, substituted methyl styrenes, polyol acrylates or methacrylates, vinyl monomers, vinyl esters, ethylene, maleate esters, fumarate esters, itaconate esters, or the like. Some specific examples include methyl methacrylate, butyl acrylate, butyl methacrylate, hexyl acrylate, hexyl methacrylate, ethyl acrylate, ethyl methacrylate, propyl acrylate, propyl methacrylate, 2-ethylhexyl acrylate, 2-ethylhexy methacrylate, hydroxyethyl acrylate, lauryl acrylate, lauryl methacrylate, octadecyl acrylate, octadecyl methacrylate, isobornyl acrylate, isobornyl methacrylate, stearyl methacrylate, ethylene glycol dimethacrylate, diethylene glycol dimethacrylate, triethylene glycol dimethacrylate, tetrahydrofurfuryl acrylate, alkoxylated tetrahydrofurfuryl acrylate, 2-phenoxyethyl methacrylate, benzyl acrylate, ethoxylated nonyl phenol methacrylate, cyclohexyl methacrylate, trimethyl cyclohexyl methacrylate, t-butyl methacrylate, n-octyl methacrylate, tridecyl methacrylate, isodecyl acrylate, dimethyl maleate, dioctyl maleate, acetoacetoxyethyl methacrylate, diacetone acrylamide, pentaerythritol tri-acrylate, pentaerythritol tetra-acrylate, pentaerythritol tri-methacrylate, pentaerythritol tetra-methacrylate, divinylbenzene, styrene, methylstyrenes (e.g., α-methyl styrene, p-methyl styrene), 1,3-butadiene, vinyl chloride, vinylidene chloride, vinylbenzyl chloride, acrylonitrile, methacrylonitrile, N-vinyl imidazole, N-vinylcarbazole, N-vinyl-caprolactam, combinations thereof, derivatives thereof, or mixtures thereof.

The heteropolymer may be formed of at least two of the previously listed monomers, or at least one of the previously listed monomers and a higher T_(g) hydrophilic monomer, such as an acidic monomer. Examples of acidic monomers that can be polymerized in forming the latex polymer particles include acrylic acid, methacrylic acid, ethacrylic acid, dimethylacrylic acid, maleic anhydride, maleic acid, vinylsulfonate, cyanoacrylic acid, vinylacetic acid, allylacetic acid, ethylidineacetic acid, propylidineacetic acid, crotonoic acid, fumaric acid, itaconic acid, sorbic acid, angelic acid, cinnamic acid, styrylacrylic acid, citraconic acid, glutaconic acid, aconitic acid, phenylacrylic acid, acryloxypropionic acid, aconitic acid, phenylacrylic acid, acryloxypropionic acid, vinylbenzoic acid, N-vinylsuccinamidic acid, mesaconic acid, methacroylalanine, acryloylhydroxyglycine, sulfoethyl methacrylic acid, sulfopropyl acrylic acid, styrene sulfonic acid, sulfoethylacrylic acid, 2-methacryloyloxymethane-1-sulfonic acid, 3-methacryoyloxypropane-1-sulfonic acid, 3-(vinyloxy)propane-1-sulfonic acid, ethylenesulfonic acid, vinyl sulfuric acid, 4-vinylphenyl sulfuric acid, ethylene phosphonic acid, vinyl phosphoric acid, vinyl benzoic acid, 2 acrylamido-2-methyl-1-propanesulfonic acid, combinations thereof, derivatives thereof, or mixtures thereof. Other examples of high T_(g) hydrophilic monomers include acrylamide, methacrylamide, monohydroxylated monomers, monoethoxylated monomers, polyhydroxylated monomers, or polyethoxylated monomers.

In examples, the aqueous dispersion of polymer particles (latexes) may be produced by emulsion polymerization or co-polymerization of any of the previously listed monomers. Other suitable techniques, specifically for generating a core-shell structure, may be used, such as: i) grafting a hydrophilic shell onto the surface of a hydrophobic core, ii) copolymerizing hydrophobic and hydrophilic monomers using ratios that lead to a more hydrophilic shell, iii) adding hydrophilic monomer (or excess hydrophilic monomer) toward the end of the copolymerization process so there is a higher concentration of hydrophilic monomer copolymerized at or near the surface, or iv) any other method known in the art to generate a more hydrophilic shell relative to the core.

In an example, the binder is present in the combined agent in an amount ranging from about 1 wt % to about 30 wt % based on a total weight of the combined agent. In another example, the binder is present in the combined agent in an amount ranging from about 2 wt % to about 25 wt % based on the total weight of combined agent. As shown in Table 2 below, these percentages may include both active binder and other non-active components present with the binder.

In examples of the combined agent, it is desirable that the total volume fraction of solids be about 50 vol. % or less, so that the combined agent is jettable via the desired inkjet printhead (e.g., thermal inkjet printhead, piezoelectric inkjet printhead, etc.). As such, the volume fraction of the gas precursor compound and the binder may be adjusted so that together, the components do not exceed, for example, from about 40 vol. % to about 50 vol. % of the total volume of the combined agent.

An example formulation of the gas generating liquid functional agent that does include a binder, and thus may be used without a separate binding agent, is shown in Table 2. This example includes calcium carbonate as the gas precursor compound.

TABLE 2 Component Actives Target Formulation Type Specific Components (wt %) (wt %) (wt %) Co-solvent 2-methyl-1,3- 99.00 9.60 9.70 propanediol 2-pyrrolidinone 95.00 17.00 17.89 Surfactant/ Tergitol ® 15-S-7 100.00 0.90 0.90 Dispersing aid Antimicrobial Acticide ® M20 10.00 0.01 0.10 (stock solution) Gas Precursor Calcium carbonate 32.00 15.00 46.88 Compound (CaCO₃) 50 nm- 100 nm dispersion Binder Acrylic latex 41.40 9.00 21.74 dispersion Water Deionized Water — — 2.79

Binding Liquid Functional Agent

The binding liquid functional agent (i.e., binding agent) may be used to pattern build material where it is desirable to form the 3D object and where it is desirable to form the 3D support structure. The binding agent may also be used in combination with examples of the gas generating liquid functional agent that do not include a binder to pattern build material where it is desirable to form the irreversibly breakable connection.

The binding agent includes the binder. Any of the binders set forth herein for examples of the combined agent may be used in the binding agent. In an example, the binder is present in the binding agent in an amount ranging from about 1 wt % to about 30 wt % based on a total weight of the binding agent. In another example, the binder is present in the binding agent in an amount ranging from about 2 wt % to about 20 wt % based on the total weight of binding agent. These percentages may include active binder, and the percentages may be higher when other non-active components are considered (e.g., in Table 3).

In addition to the binder, the binding agent may also include water, co-solvent(s), surfactant(s) and/or dispersing aid(s), antimicrobial agent(s), and/or anti-kogation agent(s). In these examples, any of the previously described co-solvent(s), surfactant(s) and/or dispersing aid(s), antimicrobial agent(s), and/or anti-kogation agent(s) may be used in any of the given amounts, except that the weight percentages are with respect to a total weight of the binding agent.

The composition of the binding liquid functional agent is similar to examples of the gas generating liquid functional agent except that the gas precursor compound(s) is excluded from the formulation of the binding liquid functional agent.

An example formulation of the binding liquid functional agent is shown in Table 3.

TABLE 3 Component Actives Target Formulation Type Components (wt %) (wt %) (wt %) Co-solvent 2-methyl-1,3- 99.00 9.60 9.70 propanediol 2-pyrrolidinone 95.00 17.00 17.89 Surfactant/ Tergitol ® 15-S-7 100.00 0.90 0.90 Dispersing aid Antimicrobial Acticide ® M20 10.00 0.01 0.1 (stock solution) Binder Acrylic latex 41.40 16.00 38.65 dispersion Water Deionized Water — — Balance

Methods

An example of the 3D printing method 100, in which a gas generating liquid functional agent and a binding agent are used, is depicted in FIG. 1. Generally, the method 100 includes patterning build material layers to form an intermediate structure, the patterning including: selectively applying a binding agent to define: a build material support structure and a patterned intermediate part; and selectively applying i) the binding agent and a separate agent including a gas precursor or ii) a combined agent including a binder and the gas precursor to define a patterned breakable connection between at least a portion of the build material support structure and at least a portion of the patterned intermediate part (reference numeral 102); and heating the intermediate structure to a temperature that activates the gas precursor to create gas pockets in the patterned breakable connection (reference numeral 104).

Any examples of the build material, the binding agent, and the gas generating liquid functional agent described herein may be used in the method 100. Furthermore, the method 100 may be used to form 3D objects, 3D support structures, and irreversibly breakable connections of any size and/or shape, as long as the irreversibly breakable connection is located between at least a portion of the 3D object and the 3D support structure, and provides a breakable junction between the 3D object and the 3D support structure.

At reference numeral 102 in FIG. 1, build material layers are patterned to form the intermediate structure, which is ultimately heated to form the 3D object, 3D support structure, and irreversibly breakable connection. FIGS. 2A through 2D depict various examples of the intermediate structures 40A, 40B, 40C, 40D that may be made using the method 100.

In an example, patterning the build material layers includes: iteratively applying individual build material layers 12, 12A, 12B, etc.; selectively applying the binding agent to at least some, or to each, of the individual build material layers to define several layers of the build material support structure 23 and several layers of the patterned intermediate part 25; and selectively applying i) the binding agent and the separate agent or ii) the combined agent on each of the individual build material layers to define the patterned breakable connection between the several layers of the build material support structure 23 and the several layers of the patterned intermediate part 25. In some examples (e.g., FIGS. 2A and 2D), the patterned breakable connection 23 alone separates the build material support structure 23 from the patterned intermediate part 25, and in other examples (e.g., FIGS. 2B and 2C), one or more layers of non-patterned build material 28 and the patterned breakable connection 23 separate the build material support structure 23 from the patterned intermediate part 25.

In the examples shown in FIGS. 2A through 2D, several build material layers 12, 12A, 12B . . . 12H (FIG. 2A), etc. have been applied and patterned to define different examples of the build material support structure 23, the patterned intermediate part 25, and the patterned breakable connection 32. Repeated application and patterning may be performed until the total number of build material layers that are patterned form a complete build material support structure 23 according to a 3D model of the 3D support structure, a complete patterned intermediate part 25 according to a 3D model of the 3D object, and a complete patterned breakable connection 32 according to a 3D model of the irreversibly breakable connection.

The build material 14 may be spread to form the layers 12, 12A, 12B, etc. on a build area platform 16, and the respective layers 12, 12A, 12B, etc. may be patterned with the binding agent and/or an example of the gas generating liquid functional agent one layer at a time. Examples of the spreading of the build material 14 and the application of the various agents to pattern are described in more detail in reference to FIGS. 4A-4J. The agent(s) used to pattern any individual build material layer 12, 12A, 12B, etc. will depend upon whether the patterned portion is part of the build material support structure 23, the patterned intermediate part 25, or the patterned breakable connection 32. The binding agent is used to pattern the build material support structure 23 and the patterned intermediate part 25, and either i) the binding agent and the separate agent including the gas precursor or ii) the combined agent including both the binder and the gas precursor is used to pattern the patterned breakable connection 32.

As shown in FIGS. 2A through 2C, the patterned breakable connection 32 is defined between at least a portion of the build material support structure 23 and the patterned intermediate part 25. In these examples, the build material support structure 23 provides support for at least some of the build material 14 of the patterned intermediate part 25 during the patterning process and during the subsequent heating process. Also in these examples, the patterned intermediate part 25 at least partially overlies the build material support structure 23.

In the example shown in FIG. 2A, the patterned breakable connection 32 is built up vertically between one surface of the build material support structure 23 and one surface of the patterned intermediate part 25, and then is curved so that it overlies a portion of the build material support structure 23. In this example, the build material support structure 23 provides support at least for the curved portion of the patterned intermediate part 25. To form this intermediate structure 40A, the binder agent is selectively applied on layers 12 through 12H to define the patterned intermediate part 25; the binder agent is selectively applied on layers 12 through 12D to define the build material support structure 23; and either i) the binding agent and the separate agent including the gas precursor or ii) the combined agent is selectively applied on layers 12 through 12E to define the patterned breakable connection 32.

In the example shown in FIG. 2B, the patterned breakable connection 32 is horizontally defined between one surface of the build material support structure 23 and one surface of the patterned intermediate part 25. In this example, the patterned breakable connection 32 completely overlies the build material support structure 23, which provides support for the overlying portion of the patterned intermediate part 25. To form this intermediate structure 40B, the binder agent is selectively applied on layers 12 through 12W to define the patterned intermediate part 25; the binder agent is selectively applied on layers 12 through 12R to define the build material support structure 23; and either i) the binding agent and the separate agent including the gas precursor or ii) the combined agent is selectively applied on layers 12S and 12T to define the patterned breakable connection 32. Also in this example, some of the build material 14 between the patterned intermediate part 25 and the build material support structure 23 remains non-patterned (shown at reference numeral 28). The non-patterned build material 28 can be easily removed after patterning and before heating, and thus can create a space between the patterned intermediate part 25 and the build material support structure 23.

In the example shown in FIG. 2C, the patterned breakable connection 32 is built up vertically between one surface of the build material support structure 23 and a portion of one surface of the patterned intermediate part 25. To form this intermediate structure 40C, the binder agent is selectively applied on layers 12 through 12H to define the patterned intermediate part 25; the binder agent is selectively applied on layers 12C through 12E to define the build material support structure 23; and either i) the binding agent and the separate agent including the gas precursor or ii) the combined agent is selective applied on layers 12C through 12E to define the patterned breakable connection 32. Also in this example, some of the build material 14 between the patterned intermediate part 25 and the build material support structure 23 remains non-patterned 28, and thus can create spaces between the patterned intermediate part 25 and the build material support structure 23. In this example, the build material support structure 23, in combination with the non-patterned build material 28, provides support for the overlying portion of the patterned intermediate part 25 formed thereon during patterning.

In the example shown in FIG. 2C, the intermediate structure 40C can be extracted from any non-patterned build material 14, 28 surrounding the structure 40C and in the spaces, and then rotated (e.g., 90°) so that the build material support structure 23 contacts a surface of a heating mechanism and so that the curved center portion of the horseshoe or C-shaped part is substantially parallel to the surface of the heating mechanism. In these examples, the build material support structure 23 provides support for a different portion of the patterned intermediate part 25 during heating than during patterning.

As shown in FIG. 2D, the patterned breakable connection 32 is defined between the build material support structure 23 and the patterned intermediate part 25. In this example, the patterned breakable connection 32 is at least partially perpendicular to the build area platform 16. In this and other similar examples, the build material support structure 23 may be next to the patterned breakable connection 32, which is next to the patterned intermediate part 25 on the build area platform 16. In these examples, there is no non-patterned build material 28 between the build material support structure 23 and the patterned intermediate part 25, and the patterned intermediate part 25 does not overly the build material support structure 23 during patterning.

In the example shown in FIG. 2D, the intermediate structure 40D can be extracted from any non-patterned build material 14, 28 surrounding the structure 40D, and then rotated (e.g., 90°) so that the build material support structure 23 contacts a surface of a heating mechanism and the patterned breakable connection 32 is at least partially parallel to the surface of the heating mechanism. In these examples, the build material support structure 23 provides support for the patterned intermediate part 25 during heating, but not during the printing/patterning process.

Several examples of the intermediate structure 40 and the patterned breakable connection 32 have been illustrated in FIGS. 2A through 2D. It is to be understood that the components 23, 25, 32 of the intermediate structure 40 may have other configurations, as long as the geometry of the irreversibly breakable connection can be broken to separate the 3D object from the 3D support structure.

Another, more specific example of the 3D printing method, shown at reference numeral 200, is depicted in FIG. 3. Generally, the method 200 includes patterning a build material layer by selectively applying a binding agent to define: a layer of a build material support structure and a layer of a patterned intermediate part separated by non-patterned build material (reference numeral 202); applying another layer of build material on the patterned build material layer (reference numeral 204); patterning the other layer of build material by: selectively applying i) the binding agent and a separate agent including a gas precursor or ii) a combined agent including a binder and the gas precursor on a portion of the other layer of build material that overlies the build material support structure, thereby forming a patterned breakable connection (reference numeral 206); selectively applying the binding agent on another portion of the other layer of build material to define an outer layer of a region of the patterned intermediate part (reference numeral 208); forming a remaining region of the patterned intermediate part on the patterned breakable connection and in contact with the region of the patterned intermediate part, thereby forming an intermediate structure including the patterned intermediate part and the build material support structure temporarily bound together at the patterned breakable connection (reference numeral 210); and heating the intermediate structure to a temperature that activates the gas precursor to create gas pockets in the patterned breakable connection (reference numeral 212).

Any examples of the build material, the binding agent, and the gas generating liquid functional agent described herein may be used in the method 200.

It is to be understood that the method 200 shown in FIG. 3 will be discussed in detail in conjunction with FIGS. 4A through 4J, and FIG. 5.

As shown in reference numeral 202, the method 200 includes patterning a build material layer by selectively applying a binding agent to define a layer of a build material support structure and a layer of a patterned intermediate part, where the patterned layers are separated by non-patterned build material. An example of the patterning of the build material layer is shown in cross-section in FIG. 4A. Prior to patterning, build material particles 14 may be applied to form a build material layer 12, and then the layer 12 may be patterned. In the example shown in FIG. 4A, one build material layer 12 including build material particles 14 has been deposited on (i.e., applied to, formed on, etc.) a build area platform 16 and patterned.

Forming and patterning the build material layer 12 may include the use of a printing system (an example of which is shown at reference numeral 60 in FIG. 5). The printing system 60 may include the build area platform 16, a build material supply 11 containing build material particles 14, a build material distributor 13, and an applicator 17.

The build area platform 16 receives the build material particles 14 from the build material supply 11. The build area platform 16 may be moved in the directions as denoted by the arrow 15 (FIG. 5), e.g., along the z-axis, so that the build material particles 14 may be delivered to the build area platform 16 or to a previously patterned layer (see, e.g., FIG. 4C). In an example, when the build material particles 14 are to be delivered, the build area platform 16 may be programmed to advance (e.g., downward) enough so that the build material distributor 13 can push the build material particles 14 onto the build area platform 16 to form a substantially uniform build material layer 12 thereon. The build area platform 16 may also be returned to its original position, for example, when a new object is to be built.

The build material supply 11 may be a container, bed, or other surface that is to position the build material particles 14 between the build material distributor 13 and the build area platform 16.

The build material distributor 13 may be moved in the directions as denoted by the arrow 15′ (FIG. 5), over the build material supply 11 and across the build area platform 16 to spread the build material particles 14 over the build area platform 16. The build material distributor 13 may also be returned to a position adjacent to the build material supply 11 following the spreading of the build material particles 14. The build material distributor 13 may be a blade (e.g., a doctor blade), a roller, a combination of a roller and a blade, and/or any other device capable of spreading the build material 16 over the build area platform 16. For instance, the build material distributor 13 may be a counter-rotating roller. In some examples, the build material supply 11 or a portion of the build material supply 11 may translate along with the build material distributor 13 such that build material particles 14 are delivered continuously to the material distributor 13, rather than being supplied from a single location (as shown in FIG. 5).

A controller (shown as 62 in FIG. 5) may process build material supply data, and in response, may control the build material supply 11 to appropriately position the build material particles 14, and may process spreader data, and in response, may control the build material distributor 13 to spread the supplied build material particles 14 over the build area platform 16 to form the build material layer 12 thereon. As shown in FIG. 4A, one build material layer 12 has been formed. The layers 12, 12A, etc. shown in FIGS. 2A through 2D may be formed in a similar manner.

The build material layer 12 has a substantially uniform thickness across the build area platform 16. In an example, the thickness of the build material layer 12 ranges from about 90 μm to about 110 μm, although thinner or thicker layers may be used. For example, the thickness of the build material layer 12 may range from about 50 μm to about 200 μm. In another example, the thickness of the build material layer 12 ranges from about 30 μm to about 300 μm. In yet another example, the thickness of the build material layer 12 may range from about 20 μm to about 500 μm. The layer 12 thickness may be about 2× (i.e., 2 times) the particle diameter at a minimum for finer part definition. In some examples, the layer 12 thickness may be about 1.2× the particle diameter.

A binding agent 18 is selectively applied to different portions of the build material layer 12 in order to pattern the layer 12. The different portions 20, 24 of the build material layer 12 to which the binding agent 18 is selectively applied may be respectively defined by a 3D model of the support structure that is to be formed and a 3D model of the 3D object that is to be formed. In FIG. 4A, the binding agent 18 is selectively applied to the portion/area 20 of the build material layer 12 to define one patterned layer 22 (shown in FIG. 4B) of a build material support structure 23 (shown in FIG. 4D), and the binding agent 18 is selectively applied to the portion(s)/area(s) 24 of the build material layer 12 to define one patterned layer 26 (shown in FIG. 4B) of a patterned intermediate part 25 (shown in FIG. 4F).

The applicator 17 may be used to selectively apply the binding agent 18. The applicator 17 may include nozzles, fluid slots, and/or fluidics for dispensing the binding agent 18. The applicator 17 may be a thermal inkjet printhead or print bar, a piezoelectric printhead or print bar, or a continuous inkjet printhead or print bar. While a single applicator 17 is shown in FIG. 4B, it is to be understood that multiple applicators 17 may be used.

The applicator 17 may be scanned across the build area platform 16, for example, in the directions as denoted by the arrow 15″ in FIG. 5. The applicator 17 may extend a width of the build area platform 16. The applicator 17 may also be scanned along the x-axis, for instance, in configurations in which the applicator 17 does not span the width of the build area platform 16 to enable the applicator 17 to deposit the binding agent 18 over a large area of a build material layer 12. The applicator 17 may thus be attached to a moving XY stage or a translational carriage that moves the applicator 17 adjacent to the build area platform 16 in order to deposit the binding agent 18 in predetermined areas 20, 24 of the build material layer 12.

The applicator 17 may deliver drops of the binding agent 18 at a resolution ranging from about 300 dots per inch (DPI) to about 1200 DPI. In other examples, the applicator 17 may deliver drops of the binding agent 18 at a higher or lower resolution. The drop velocity may range from about 5 m/s to about 24 m/s and the firing frequency may range from about 1 kHz to about 100 kHz. In one example, the volume of each drop may be in the order of about 3 picoliters (pl) to about 18 pl, although it is contemplated that a higher or lower drop volume may be used. In some examples, the applicator 17 is able to deliver variable drop volumes of the binding agent 18. One example of a suitable printhead has 600 DPI resolution and can deliver drop volumes ranging from about 6 pl to about 14 pl.

The binding agent 18 is deposited interstitially in the openings or voids between the build material particles 14. Capillary flow can move the binding agent 18 between the individual build material particles 14 in the areas 20, 24.

In this example, it is desirable for the patterned layers 22, 26 to be separated by non-patterned build material 28, (i.e., particles 14 without any binding agent 18 applied thereto) so that the layers 22, 26 are not in direct contact with one another. The non-patterned build material 28 is not intended to be used in forming the build material support structure 23 or the patterned intermediate part 25. In this example, as shown in FIGS. 4A and 4B, some of the non-patterned build material 28 is located at the outer edges of the patterned layer 26 of the patterned intermediate part 25. The build material particles 14 that are directly adjacent to the edges of the build area platform 16 may be exposed to a different environment (a metal wall, air, etc.) than the build material particles 14 that are surrounded by other build material particles 14. The different environment can lead to non-uniformity at the edges. As such, it may be desirable to have non-patterned build material 28 at the outer edges of the patterned layer 26.

Referring specifically now to FIG. 4B, the selective application of the binding agent 18 onto the build material particles 14 within the area 24 results in the formation of a patterned layer 26, which is to become part of a patterned intermediate part 25 (FIG. 4F), which is ultimately to be sintered to form the 3D object/part. More particularly, in the example shown in FIG. 4B, the patterned layer 26 is the first layer of the 3D object being formed. Similarly, as shown in FIG. 4B, the selective application of the binding agent 18 onto the build material particles 14 within the area 20 results in the formation of a patterned layer 22, which is to become part of the build material support structure 23 (FIG. 4D). More particularly, in the example shown in FIG. 4B, the patterned layer 22 is the first layer of the build material support structure 23 being formed.

In examples of the method 200 where the build material support structure 23 is a single layer, the method 200 may continue with reference numerals 204 and 206 of FIG. 3. In other examples, the build material support structure 23 (FIG. 3D) is a multi-layer structure, and thus the method 200 may further include iteratively applying additional build material layers (e.g., 12A, 12B, 12C, shown in FIG. 4C) and selectively applying the binding agent 18 to the additional build material layers 12A, 12B, 12C to define several layers of the build material support structure 23 and several layers of a region 27 of the patterned intermediate part 25, wherein the several layers of the build material support structure 23 and the several layers of the region 27 of the patterned intermediate part 25 are separated by additional non-patterned build material 28.

FIG. 4C depicts the repeated application of build material particles 14 to form the other build material layers 12A, 12B, 12C and the repeated patterning of these additional build material layers 12A, 12B, 12C over the first layer 12 of patterned build material. As mentioned above and as shown in FIG. 4D, repeated application and patterning may be performed to iteratively build additional layers of the build material support structure 23, as well as additional layers of the region 27 of the patterned intermediate part 25. Repeated application and patterning may be performed until the total number of build material layers 30 that are patterned form a complete build material support structure 23 according to a 3D object model of a 3D support structure 48 (FIG. 4I). As such, the total number of build material layers 30 that are patterned will depend on the desired dimensions of the build material support structure 23 and the ultimately formed 3D support structure 48. In the example depicted in FIGS. 4C and 4D, four build material layers 12, 12A, 12B, 12C are applied and patterned to form the complete build material support structure 23.

As shown in reference numerals 204, 206, and 208 of FIG. 3 and in FIGS. 4D and 4E, after the desired total number of build material layers 30 are patterned to form the build material support structure 23, the method 200 continues by applying another layer of build material 12D (reference numeral 204), and patterning this other build material layer 12D. Patterning the layer 12D may be accomplished by selectively applying (i) the binding agent 18 and a separate agent 21 including a gas precursor and not including a binder (i.e., one example of the gas generating liquid functional agent disclosed herein), or (ii) a combined agent 19 including the binder and the gas precursor (i.e., another example of the gas generating liquid functional agent disclosed herein) on a portion of the other layer 12D of build material that overlies the build material support structure 23, thereby forming a patterned breakable connection 32 (reference numeral 206); and selectively applying the binding agent 18 on another portion of the other layer 12D of build material to define an outer layer 34 of the region 27 of the patterned intermediate part 25 (reference numeral 208).

Any example of the binding agent 18 described herein may be utilized in combination with any example of the separate gas generating liquid functional agent 21 that does not include a binder in order to define the patterned breakable connection 32. The binder from the binding agent 18 can temporarily bind the build material particles 14 of the patterned breakable connection 32 and the gas precursor of the separate gas generating liquid functional agent 21 forms gas pockets 36 (FIGS. 4H and 4I) within the irreversibly breakable connection 38 (FIG. 4I) that is formed during sintering.

When the agents 18 and 21 are used to define the patterned breakable connection 32, the binding agent 18 may be dispensed from the applicator 17, and the separate gas generating liquid functional agent 21 may be dispensed from a separate applicator. The separate applicator may be similar to applicator 17 (i.e., may be a thermal inkjet printhead, a piezoelectric printhead, etc.), and may be operated in the same manner as previously described herein. In another example, the applicator 17 may have separate chambers that contain the binding agent 18 and the separate gas generating liquid functional agent 21, and may also have separate printheads, nozzles, etc. to separately and selectively dispense the two agents 18, 21. In these examples, the applicator(s) may be programmed to receive commands from the controller 62 and to deposit the agents 18 and 21 according to a 3D object model of the irreversibly breakable connection 38. In the example shown in FIG. 2D, the applicator(s) sequentially or simultaneously apply the agents 18 and 21 to the build material particles 14 of the layer 12D which overly the build material support structure 23. This defines the patterned breakable connection 32 on a surface of the build material support structure 23. The agents 18 and 21 are deposited interstitially in the openings or voids between the build material particles 14. Capillary flow can move the agents 18 and 21 between the individual build material particles 14 in the layer 12D.

Alternatively, any example of the combined agent 19, including both the binder and the gas precursor, may be used to define the patterned breakable connection 32. When the combined agent 19 is used, a separate binding agent 18 is not utilized to define the patterned breakable connection 32. In these examples, the binder from the combined agent 19 can temporarily bind the build material particles 14 of the patterned breakable connection 32 and the gas precursor of the combined agent 19 forms gas pockets 36 (FIGS. 4H and 4I) within the irreversibly breakable connection 38 (FIG. 4I) that is formed during sintering.

When the combined agent 19 is used to define the patterned breakable connection 32, the combined agent 19 may be dispensed from an applicator that is similar to applicator 17 (i.e., may be a thermal inkjet printhead, a piezoelectric printhead, etc.), and that may be operated in the same manner as previously described herein for the applicator 17. In another example, the applicator 17 may have separate chambers that contain the combined agent 21 and the binding agent 18 (e.g., used to pattern the build material support structure 23 and the patterned intermediate part 25), and may also have separate printheads, nozzles, etc. for separately and selectively dispensing the two agents 19, 18. In these examples, the applicator may be programmed to receive commands from the controller 62 and to deposit the combined agent 19 according to a 3D object model of the irreversibly breakable connection 38. In the example shown in FIG. 4D, the applicator applies the agent 19 to the build material particles 14 of the layer 12D which overly the build material support structure 23. This defines the patterned breakable connection 32 on a surface of the build material support structure 23. The combined agent 19 is deposited interstitially in the openings or voids between the build material particles 14. Capillary flow can move the agent 19 between the individual build material particles 14 in the layer 12D.

Also in the example shown in FIG. 4D, the applicator 17 selectively applies the binding agent 18 on those portion(s) of the build material layer 12D in order to define the outer layer 34 of the region 27 of the patterned intermediate part 25. In these examples, the applicator 17 may be programmed to receive commands from the controller 62 and to deposit the binding agent 18 according to a 3D object model of the 3D object being formed.

As shown at reference numeral 210 in FIG. 3 and in FIGS. 4E and 4F, the method 200 further includes forming a remaining region 29 of the patterned intermediate part 25 on the patterned breakable connection 32 and in contact with the (previously patterned) region 27 of the patterned intermediate part 25, thereby forming an intermediate structure 40 including the patterned intermediate part 25 and the build material support structure 23, temporarily bound together at the patterned breakable connection 32. The remaining region 29 of the patterned intermediate part 25 is formed by applying a further layer 12E of build material on the patterned breakable connection 32 and the outer layer 34 of the region 27 of the patterned intermediate part 25, and selectively applying the binding agent 18 to the further layer 12E to define a patterned layer 42 of the remaining region 29 of the patterned intermediate part 25. This patterned layer 42 of the remaining region 29 is in direct contact with at least some of the region 27, so that the two regions 27, 29 can be sintered together to form the 3D object. Moreover, this patterned layer 42 of the remaining region 29 overlies the patterned breakable connection 32 and the support structure 23, both of which provide physical support to the patterned layer 42 and any other layers applied and patterned to form the remaining region 29.

In examples of the method 200 where the remaining region 29 is a single layer, the method 200 may continue with reference numeral 212 of FIG. 3. In other examples, the remaining region 29 (FIG. 4F) is a multi-layer structure, and thus the method 100 may further include iteratively applying additional build material layers (e.g., 12E, 12F, 12G, 12H shown in FIG. 4F) and selectively applying the binding agent 18 to the additional build material layers 12E, 12F, 12G, 12H to define several layers of the remaining region 29 of the patterned intermediate part 25.

After the layer(s) 12E, 12F, 12G, 12H of the remaining region 29 are patterned, the intermediate structure 40 is formed. The intermediate structure 40 is similar to intermediate structures 40, 40A, 40B, 40C, or 40D, in that each of the structures 40, 40A, 40B, 40C, 40D includes the patterned intermediate part 25, the build material support structure 23, and the patterned breakable connection 32 which temporarily binds the patterned intermediate part 25 and the build material support structure 23. As such, the following discussion of evaporation and heating may be applicable for both methods 100 and 200, and for any intermediate structure 40, 40A, 40B, 40C, 40D that may be formed.

In any of the examples disclosed herein, the intermediate structure 40, 40A, 40B, 40C, 40D may be part of a build material cake including the intermediate structure 40, 40A, 40B, 40C, 40D and any non-patterned build material 28. In the example shown in FIG. 4F, the non-patterned build material 28 may be positioned between surfaces of the patterned intermediate part 25 and surfaces of the build material support structure 23 and/or surrounding the patterned intermediate part 25.

During and/or after the formation of the intermediate structure 40, 40A, 40B, 40C, 40D, the liquid components of the binding agent 18, and the separate agent 21 or the combined agent 19 may be at least substantially evaporated to form a densified intermediate part 25′, a densified build material support structure 23′, and a densified patterned breakable connection 23′ (which together make up the densified intermediate structure 40′ shown in FIG. 4G). In some examples, the liquid components (e.g., water, solvents) may be substantially evaporated during the layer by layer patterning process and/or while the intermediate structure 40′ is on the build area platform, and thus a post excavation baking process may not be used. In these examples, additional heating may be used in order to remove water and solvents, which may activate the binder to generate a densified intermediate structure 40′. In other examples, enough of the liquid components may be evaporated in the layer by layer patterning process and/or while the intermediate structure 40′ is on the build area platform to render the structure 40′ handleable, and then a post excavation baking process may be used to remove additional solvent and activate the binder to generate the densified intermediate structure 40′.

It is to be understood that at least substantial evaporation of the liquid components may be partial evaporation or complete evaporation. At least substantial evaporation may be partial evaporation when the presence of residual liquid components does not deleteriously affect the desired structural integrity of the intermediate structure 40 or the final 3D object that is being formed. As an example, the densified intermediate part 25′ formed by the at least substantial evaporation of the liquid components of the agent(s) 18 may contain a residual amount of the agent 18, but the agent 18 is completely removed during subsequent heating.

As mentioned, at least substantial evaporation of the liquid components (e.g., water and solvents) activates the binder in the binding agent 18, and when used, in the combined agent 19. For example, accelerated evaporation and binder activation may occur when heating to a glass transition temperature or a minimum film formation temperature of the binder. When activated, the binder coalesces and forms a polymer glue that coats and binds together the build material particles 14 patterned with the binding agent 18, and when used, the combined agent 19. At least substantial evaporation of the liquid components also may result in the densification of the patterned build material particles 14 through capillary compaction. As such, at least substantial evaporation forms the densified intermediate structure 40′, shown in FIG. 4G.

In an example when an acrylic latex is used as the binder, a first solvent of the binding agent 18 and/or combined agent 21 may evaporate and allow a second solvent of the binding agent 18 and/or combined agent 21 to come into contact with and soften the acrylic latex particles. Then, as the second solvent evaporates, the softened acrylic latex particles may merge or coalesce to form the continuous network or film to bind the patterned volumes of build material particles 14 into, for example, a densified intermediate part 25′, a densified build material support structure 23′, and a densified patterned breakable connection 32′ (which together make up the densified intermediate structure 40′ shown in FIG. 4G).

The liquid components may be volatile enough to evaporate at ambient temperature, or the densification/evaporation temperature may be above ambient temperature. As used therein, “ambient temperature” may refer to room temperature (e.g., ranging about 18° C. to about 22° C.), or to the temperature of the environment in which the 3D printing method is performed (e.g., the temperature of the build area platform 16 during the forming and patterning of new layers). The temperature of the environment in which the 3D printing method is performed (e.g., the temperature of the build area platform 16 during the forming and patterning of new layers) is about 5° C. to about 50° C. below the boiling point of the agent 18 and 19 or 21. In an example, the temperature of the build area platform 16 during the forming and patterning of new layers ranges from about 50° C. to about 95° C. Other examples of the 3D printing environment temperature may range from about 40° C. to about 65° C. The densification/evaporation temperature may also be below a temperature at which the binder would be damaged (i.e., be unable to bind). For a majority of suitable binders, the upper limit of the densification/evaporation temperature ranges from about 180° C. to about 220° C. Above this temperature threshold, the binder would chemically degrade into volatile species and leave the patterned components 23, 25, 32, and thus would stop performing their function. For some agents 18, and when used 19, the densification/evaporation temperature ranges from about 50° C. to about 220° C. As still another example, the densification/evaporation temperature may range from about 70° C. to about 90° C.

During evaporation, the gas precursor (in the patterned breakable connection 32) can collect across the surfaces of the build material particles 14 in the patterned breakable connection 32.

In some examples of the method 100 or 200, the binding agent 18, and when used, the combined agent 19, may be allowed to evaporate without heating. For example, more volatile solvents can evaporate in seconds at ambient temperature. In these examples, the build material cake is not exposed to heat or radiation to generate heat, and the water and/or solvent(s) in the binding agent 18, and when used, in the combined agent 19 evaporate(s) over time. In an example, the water and/or solvent(s) in the binding agent 18, and when used, the combined agent 19 may evaporate without heating within a time period ranging from about 1 second to about 1 minute.

In other examples of the method 100 or 200, the intermediate structure 40, 40A, 40B, 40C, 40D may be heated to an evaporation temperature at a rate of about 1° C./minute to about 10° C./minute, although it is contemplated that a slower or faster heating rate may be used. The heating rate may depend, in part, on one or more of: the agents 18, 19, 21 used, the size (i.e., thickness and/or area (across the x-y plane)) of the layers, and/or the characteristics of the structure 40, 40A, 40B, 40C, 40D (e.g., size, wall thickness, etc.). In an example, intermediate structure 40, 40A, 40B, 40C, 40D is heated to the densification/evaporation temperature at a rate of about 2.25° C./minute.

At least substantially evaporating (with or without heating) activates the binder, and the activated binder provides enough adhesive strength to hold the densified intermediate structure 40′ together with enough mechanical stability to survive removal from the build material cake. As such, the densified intermediate structure 40′ exhibits handleable mechanical durability, and is capable of being separated from the non-patterned build material 28. FIG. 4G depicts the densified intermediate structure 40′ after the non-patterned build material 18 has been removed.

If after excavation from the build area platform 16, the densified intermediate structure 40′ still contains an undesirable amount of less-volatile solvent(s), the post-excavation baking may be performed at a temperature that will evaporate these solvent(s).

While not shown, it is to be understood that the intermediate structures 40A, 40B, 40C, 40D may be densified in a similar manner.

The densified intermediate structure 40′ may be extracted from the build material cake or separated from the non-patterned build material 28 by any suitable means. In an example, the densified intermediate structure 40′ may be extracted by lifting the densified intermediate structure 40′ from the non-patterned build material 28. Any suitable extraction tool may be used. In some examples, the densified intermediate structure 40′ may be cleaned to remove non-patterned build material 28 from its surface. In an example, the densified intermediate structure 40′ may be cleaned with a brush and/or an air jet, may be exposed to mechanical shaking, or may be exposed to other techniques that can remove the non-patterned build material 28. As shown in FIG. 4G, removal of the non-patterned build material 28 can expose outer edges of the densified intermediate structure 40′ and any spaces 50 between the densified build material support structure 23′ and portions of the densified patterned intermediate part 25′ that had been occupied by the non-patterned build material 28 during the printing process.

When the densified intermediate structure 40′ is extracted from the build material cake and/or cleaned of the non-patterned build material 28, the densified intermediate structure 40′ may be removed from the build area platform 16 and placed in a heating mechanism 44 (as shown in FIG. 4H).

The heating mechanism 44 may be used to perform a heating sequence, which involves exposing the intermediate structure 40′ (or the densified version of the intermediate structures 40A, 40B, 40C, or 40D) to a temperature that activates the gas precursor to create gas pockets 36 in the patterned breakable connection 32. The heating sequence may form a 3D particle article 10, as shown in FIG. 4I. In some examples, heating involves exposure to a series of temperatures that form a 3D object 46 from the patterned intermediate part 25, 25′, a 3D support structure 48 from the build material support structure 23, 23′ and the irreversibly breakable connection 38 from the patterned breakable connection 32, 32′, the irreversibly breakable connection 38 including the gas pockets 36 and being positioned between the 3D object 46 and the 3D support structure 48.

The series of temperatures may involve heating the (densified) intermediate structure 40′ (or the densified version of the intermediate structures 40A, 40B, 40C, or 40D) to a de-binding temperature, and then to an initial sintering temperature, followed by a gas pocket formation temperature, followed by a final sintering temperature. Briefly, the de-binding temperature removes the binder from the densified intermediate structure 40′ to produce an at least substantially binder-free intermediate structure, and the at least substantially binder-free intermediate structure may be sintered at the various temperatures to form the final 3D object 46, the irreversibly breakable connection 38, and the 3D support structure 48, and to create the gas pockets 36 within the irreversibly breakable connection 38. Heating to de-bind and heating to sinter and create the gas pockets 36 may take place at several different temperatures, where the temperature for de-binding is lower than the temperatures for sintering and gas pocket creation.

Heating to de-bind is accomplished at a thermal decomposition temperature that is sufficient to thermally decompose the binder. As such, the temperature for de-binding depends upon the binder in the agents 18, 19 used. In an example, the thermal decomposition temperature ranges from about 250° C. to about 600° C. In another example, the thermal decomposition temperature ranges from about 300° C. to about 550° C. The binder may have a clean thermal decomposition mechanism (e.g., leaves non-volatile residue in an amount <5 wt % of the initial binder, and in some instances non-volatile residue in an amount <1 wt % of the initial binder). The smaller residue percentage (e.g., close to 0%) is more desirable. During the de-binding stage, the binder decomposes first into a liquid phase of lower viscosity. Evaporation of this liquid may initially increase the open porosity in the substantially binder-free intermediate structure.

While not being bound to any theory, it is believed that the at least substantially binder-free intermediate structure may maintain its shape due, for example, to one or more of: i) the low amount of stress experienced by the at least substantially binder-free i part due to it not being physically handled, and/or ii) low level necking occurring between the build material particles 14 at the thermal decomposition temperature of the binder. The at least substantially binder-free intermediate structure may maintain its shape although the binder is at least substantially removed and the build material particles 14 are not yet sintered.

The temperature may be raised to begin the initial stages of sintering of the substantially binder-free intermediate structure, which can result in the formation of weak bonds that are strengthened during final sintering. The initial sintering temperature is selected to further densify the substantially binder-free intermediate structure and to decrease or eliminate the open porosity throughout the substantially binder-free intermediate structure. Open pores are pores that are interconnected to other pores, and thus can undesirably allow gas(es) generated by the gas precursor to be vented out of the patterned breakable connection 32 as it is sintered to form the irreversibly breakable connection 38. The initial sintering temperature may be well above the de-binding temperature, may be capable of softening the build material particles 14, and may be below the activation temperature of the gas precursor, so that the open pores are transformed into closed pores (through the build material particles 14 beginning to sinter together) and so that gas(es) are not yet generated by the gas precursor. As such, the initial sintering temperature allows the build material particles 14 in the patterned breakable connection 32 to soften and merge together enough to surround or enclose the gas precursor without generating pocket forming gases.

The initial sintering temperature may thus be dependent upon the build material used, as well as the gas precursor in the agent 19 or 21 used to pattern the patterned breakable connection 32. Moreover, the initial sintering temperature may also be dependent on the sintering rate of build material. For example, metal powders with a smaller particle size can be sintered at a higher rate at lower temperatures than the same metal powders with a larger particle size. In this example, the previously described open to closed porosity transition in the breakable connection 38 created from smaller particle size metal powders may occur relatively rapidly at lower temperatures, which enables the use of a lower initial sintering temperature.

The heating temperature may then be raised to activate the gas precursor in order to create/form the gas pockets 36 at the patterned breakable connection 32 and in the irreversibly breakable connection 38. Sintering has been initiated to form the 3D object 46, 3D support structure 48, and the irreversibly breakable connection 38, which means that the build material particles 14 of the patterned breakable connection 32 have begun to coalesce and that open pores (i.e., pores that connect to other pores) have begun to transform to closed pores (i.e., pores completely surrounded by coalesced build material). As such, the gas precursor is either residing inside the bulk build material particles 14 or is trapped inside the closed pores, and thus is isolated from open porosity. Thus, the gas precursor may be activated, as the generated gas will be trapped within the irreversibly breakable connection 38.

The gas pocket formation temperature may be dependent upon the properties of build material. The gas pocket formation temperature may be below the final sintering temperature and the melting temperature of the build material. For example, when aluminum/aluminum alloy build materials (melting temperature may be as low as about 550° C.) are used, it may be desirable for the gas pocket activation or formation temperature to be within the range of from about 500° C. to about 590° C., and the gas precursor may be selected accordingly. As an example, titanium hydride may be a suitable gas precursor to be used with aluminum build material. For another example, when ferrous build material is used, it may be desirable for the gas pocket activation or formation temperature to be within the range from about 900° C. to about 1400° C., and the gas precursor may be selected accordingly.

The gas pocket formation temperature may also be dependent on the sintering rate of the build material. As previously described herein, metal powders with a smaller particle size can be sintered at a higher rate and at lower temperatures than the same metal powders with a larger particle size, and thus the open to closed porosity transition may occur relatively rapidly at lower temperatures. This would enable the use of gas precursors with lower activation temperatures. As one specific example, a stainless steel alloy build material having a particle size distribution of D10=8.92 μm, D50=14.8 μm, and D90=23.25 μm may have a gas pocket formation temperature ranging from about 1100° C. to about 1390° C. For smaller particle size distributions of the stainless steel alloy build material, the gas pocket formation temperature will shift to temperatures lower than 1100° C.

The following are some other examples of suitable gas precursors and their corresponding activation or gas pocket formation temperatures. Transition metal hydrides can generate substantial amounts of hydrogen gas at a temperature ranging from about 500° C. to about 900° C. Alkaline earth carbonates can generate carbon dioxide at a temperature ranging from about 840° C. to about 1500° C. Solid state mixtures of oxidizable species and oxidizing agents can generate carbon oxide gases, such as carbon dioxide or carbon monoxide, at temperatures ranging from about 800° C. to about 1400° C.

Heating to create the gas pockets 36 may take place in an environment/atmosphere that is compatible with the gas precursor and build material used to form the patterned breakable connection 32. As one example, when the gas precursor in the agent 19 or 21 used to pattern the patterned breakable connection 32 is titanium hydride or another transition metal hydride, a hydrogen gas (H₂) environment may be used during heating. As another example, when the gas precursor in the agent 19 or 21 used to pattern the patterned breakable connection 32 is an alkaline earth carbonate, any gas environment (e.g., inert, reducing, vacuum, etc.) may be used during heating. As still another example, when the gas precursor in the agent 19 or 21 used to pattern the patterned breakable connection 32 is the solid state mixture, a non-reducing environment (e.g., argon, nitrogen, or vacuum) may be used during heating.

FIG. 4H illustrates the intermediate structure 40′ during heating to the gas pocket formation temperature. As depicted, the build material particles 14 have begun to coalesce in each of the densified patterned intermediate part 25′, the densified build material support structure 23′, and the densified patterned breakable connection 32′. As such, the formation of the 3D object/part 46, the 3D support structure 48, and the irreversibly breakable connection 38 has been initiated. The initial coalescence of the build material particles 14 has formed the closed pores 52 in each of the densified patterned intermediate part 25′, the densified build material support structure 23′, and the densified patterned breakable connection 32′. Within the densified patterned breakable connection 32′, the closed pores 52 entrap the gas precursor, which has generated the gas pockets 36 as a result of being exposed to the gas pocket formation temperature.

The temperature may be raised again to finish the stages of sintering. During final sintering, the build material particles 14 continue to coalesce to form the 3D object 46, the 3D support structure 48, and the irreversibly breakable connection 38, and so that a desired density of at least the 3D object 46 is achieved. The final sintering temperature is a temperature that is sufficient to sinter the remaining build material particles 14. The sintering temperature is highly depending upon the composition of the build material particles. During final sintering, the at least substantially binder-free intermediate structure may be heated to a temperature ranging from about 80% to about 99.9% of the melting point(s) of the build material particles 14. In another example, the at least substantially binder-free intermediate structure may be heated to a temperature ranging from about 90% to about 95% of the melting point(s) of the build material particles 14. In still another example, the at least substantially binder-free intermediate structure may be heated to a temperature ranging from about 60% to about 90% of the melting point(s) of the build material particles 14. In still another example, the final sintering temperature may range from about 10° C. below the melting temperature of the build material particles 14 to about 50° C. below the melting temperature of the build material particles 14. In still another example, the final sintering temperature may range from about 100° C. below the melting temperature of the build material particles 14 to about 200° C. below the melting temperature of the build material particles 14. The final sintering temperature may also depend upon the particle size and time for sintering (i.e., high temperature exposure time). As an example, the sintering temperature may range from about 500° C. to about 1800° C. In another example, the sintering temperature is at least 900° C. An example of a final sintering temperature for bronze is about 850° C., and an example of a final sintering temperature for stainless steel is about 1400° C., and an example of a final sintering temperature for aluminum or aluminum alloys may range from about 550° C. to about 620° C. While these temperatures are provided as final sintering temperature examples, it is to be understood that the final sintering temperature depends upon the build material particles that are utilized, and may be higher or lower than the provided examples. Heating at a suitable final sintering temperature sinters and fuses the build material particles 14 to form a completed 3D object 46, a completed 3D support structure 48, and a completed irreversibly breakable connection, each of which may be even further densified relative to the corresponding components of the at least substantially binder-free intermediate structure. For example, as a result of final sintering, the density may go from 50% density to well over 90%, and in some cases very close to 100% of the theoretical density.

The length of time at which the heat (for each of de-binding, gas pocket generation, and sintering) is applied and the rate at which the structure is heated may be dependent, for example, on one or more of: characteristics of the heating mechanism 44, characteristics of the binder, characteristics of the build material particles (e.g., metal type, particle size, etc.), characteristics of the gas precursor, and/or the characteristics of the 3D object/part 46 (e.g., wall thickness).

The densified intermediate structure 40′ (or the densified version of the intermediate structures 40A, 40B, 40C, or 40D) may be heated at the de-binding temperature for a time period ranging from about 10 minutes to about 72 hours. When the structure 40′ contains open porosity to vent out binder pyrolysis, and/or the amount of the binder in the densified intermediate structure 40′ is low (e.g., from about 0.01 wt % to about 4.0 wt % based on the total weight of the build material particles 14) and/or the wall thickness of the structure 40′ is relatively thin, the time period for de-binding may be 3 hours (180 minutes) or less. Longer times may be used if the structure 40′ has less open porosity, if the structure 40′ has thicker walls, and/or if the structure 40′ has a higher concentration of binder. In an example, the de-binding time period is about 60 minutes. In another example, the de-binding time period is about 180 minutes. The densified green part may be heated to the de-binding temperature at a rate ranging from about 0.5° C./minute to about 20° C./minute. The heating rate may depend, in part, on one or more of: the amount of the binder in the densified intermediate structure 40′, the porosity of the densified intermediate structure 40′, and/or the characteristics of the densified intermediate structure 40′.

The at least substantially binder-free intermediate structure may be heated at each of the initial sintering temperature, the gas formation temperature, and the final sintering temperature for respective time periods ranging from about 20 minutes to about 15 hours. In an example, each time period is 60 minutes. In another example, each time period is 90 minutes. In still another example, each of the initial sintering time period, the gas formation time period, and the final sintering time period is less than or equal to 3 hours. The at least substantially binder-free intermediate structure may be heated to each of the initial sintering temperature, the gas formation temperature, and the final sintering temperature at a rate ranging from about 1° C./minute to about 20° C./minute. In an example, the at least substantially binder-free intermediate structure is heated to each of the initial sintering temperature, the gas formation temperature, and the final sintering temperature at a rate ranging from about 10° C./minute to about 20° C./minute. In a specific example, the at least substantially binder-free intermediate structure is heated to the initial sintering temperature at a rate of about 10° C./minute and is held at the initial sintering temperature for about 60 minutes; and then is heated to the gas formation temperature at a rate of about 10° C./minute, is held at the gas formation temperature for about 60 minutes; and then is heated to the final sintering temperature at a rate of about 10° C./minute, is held at the final sintering temperature for about 60 minutes.

An example of the resulting 3D printed article 10 is shown in FIG. 4I. After heating, the 3D printed article 10 may be cooled. It is to be understood that the gas pockets 36 remain in the irreversibly breakable connection 38 when cooled.

The 3D printed article 10 includes a first object (e.g., the 3D object 46), a second object (e.g., the 3D support structure 48), and the irreversibly breakable connection 38 between the first and second objects 46, 48, wherein the irreversibly breakable connection 38 includes the gas pockets 36. In an example, the first object is a metal 3D part, the second object is a metal 3D support structure, and the irreversibly breakable connection 38 is a metal object including the gas pockets 36.

The gas pockets 36 are localized to the irreversibly breakable connection 38, and thus add fragility to the irreversibly breakable connection 38. As such, the irreversibly breakable connection 38 provides a weak junction or a fault line domain between the first object (e.g., the 3D object 46) and the second object (e.g., the 3D support structure 48). As such, the second object (e.g., the 3D support structure 48) can be easily removed from the first object (e.g., the 3D object 46) by breaking the irreversibly breaking connection 38. Breaking may be accomplished with human hands, or with simple tools, such as pliers and/or a vise. Cutting tools may be used, but may not have to be used in order to break the second object (e.g., the 3D support structure 48) from the first object (e.g., the 3D object 46).

An example of the 3D object 46 after the irreversibly breakable connection 38 has been broken is depicted in FIG. 4J. The break at the irreversibly breakable connection 38 enables the 3D support structure 48 to be separated from the 3D object and removed (and thus it is not shown in FIG. 4J). At most, some remnants 68 of metal pieces from the irreversibly breakable connection 38 may remain attached to the 3D object 46. It is to be understood that once the irreversibly breakable connection 38 is broken, the gas within the gas pockets 36 may be released.

Printing System

Referring now to FIG. 5, an example of the 3D printing system 60 that may be used to perform examples of the method 100 disclosed herein is depicted. It is to be understood that the 3D printing system 10 may include additional components (some of which are described herein) and that some of the components described herein may be removed and/or modified. Furthermore, components of the 3D printing system 60 depicted in FIG. 5 may not be drawn to scale and thus, the 3D printing system 60 may have a different size and/or configuration other than as shown therein.

In an example, the three-dimensional (3D) printing system 60, comprises: a supply 11 of build material particles 14; a build material distributor 13; a supply of a binding agent 18 and a supply of a separate gas generating liquid functional agent 21, or a supply of a combined agent 19; applicator(s) 17 for selectively dispensing the binding agent 18 and the separate gas generating liquid functional agent 21 or the combined agent 19; a controller 62; and a non-transitory computer readable medium having stored thereon computer executable instructions to cause the controller 62 to cause the printing system to perform some or all of the method disclosed herein.

As mentioned above, the build area platform 16 receives the build material particles 14 from the build material supply 11. The build area platform 16 may be integrated with the printing system 60 or may be a component that is separately insertable into the printing system 60. For example, the build area platform 16 may be a module that is available separately from the printing system 60. The build area platform 16 that is shown is one example, and could be replaced with another support member, such as a platen, a fabrication/print bed, a glass plate, or another build surface.

While not shown, it is to be understood that the build area platform 16 may also include built-in heater(s) for achieving and maintaining the temperature of the environment in which the 3D printing method is performed.

Also as mentioned above, the build material supply 11 may be a container, bed, or other surface that is to position the build material particles 14 between the build material distributor 13 and the build area platform 16. In some examples, the build material supply 11 may include a surface upon which the build material particles 14 may be supplied, for instance, from a build material source (not shown) located above the build material supply 11. Examples of the build material source may include a hopper, an auger conveyer, or the like. Additionally, or alternatively, the build material supply 11 may include a mechanism (e.g., a delivery piston) to provide, e.g., move, the build material particles 14 from a storage location to a position to be spread onto the build area platform 16 or onto a previously patterned layer.

As shown in FIG. 5, the printing system 60 also the build material distributor 18 and the applicator(s) 17, both of which have been described in reference to the method 200.

Each of the previously described physical elements may be operatively connected to the controller 62 of the printing system 60. The controller 62 may process print data that is based on a 3D object model of the 3D object/part 46 and of the 3D support structure 48 to be generated. In response to data processing, the controller 62 may control the operations of the build area platform 16, the build material supply 11, the build material distributor 13, and the applicator(s) 17. As an example, the controller 62 may control actuators (not shown) to control various operations of the 3D printing system 62 components. The controller 60 may be a computing device, a semiconductor-based microprocessor, a central processing unit (CPU), an application specific integrated circuit (ASIC), and/or another hardware device. Although not shown, the controller 62 may be connected to the 3D printing system 60 components via communication lines.

The controller 62 manipulates and transforms data, which may be represented as physical (electronic) quantities within the printer's registers and memories, in order to control the physical elements to create the printed article 10. As such, the controller 62 is depicted as being in communication with a data store 64. The data store 64 may include data pertaining to a 3D object 46, a 3D support structure 48, and an irreversibly breakable connection 38 to be printed by the 3D printing system 60. The data for the selective delivery of the build material 16, the binding agent 18, the gas generating liquid functional agent 19 or 21, etc. may be derived from a model of the components 46, 48 and 38 to be formed. For instance, the data may include the locations on each build material layer 12, etc. that the applicator 17 is to deposit the binding agent 18. In one example, the controller 62 may use the data to control the applicator 17 to selectively apply the binding agent 18. The data store 64 may also include machine readable instructions (stored on a non-transitory computer readable medium) that are to cause the controller 62 to control the amount of build material particles 14 that is supplied by the build material supply 11, the movement of the build area platform 16, the movement of the build material distributor 13, the movement of the applicator 17, etc.

As shown in FIG. 5, the printing system 60 also includes the heating mechanism 44. Examples of the heating mechanism 44 include a conventional furnace or oven, a microwave, or devices capable of hybrid heating (i.e., conventional heating and microwave heating). As shown in FIG. 5, the heating mechanism 44 may be a module that is available separately from the printing system 60. In other examples, the heating mechanism 44 may be integrated with the printing system 60.

The heating mechanism 44 and/or the heater(s) in the build area platform 16 may be operatively connected to a driver, an input/output temperature controller, and temperature sensors, which are collectively shown as heating system components 66. The heating system components 66 may operate together to control the heating mechanism 44 and/or the heater(s) in the build area platform 16. The temperature recipe (e.g., heating exposure rates and times) may be submitted to the input/output temperature controller. During heating, the temperature sensors may sense the temperature of the build material particles 14 on the platform 16 or in the intermediate structure 40, 40′, and the temperature measurements may be transmitted to the input/output temperature controller. For example, a thermometer associated with the heated area can provide temperature feedback. The input/output temperature controller may adjust the heating mechanism 44 and/or the heater(s) in the build area platform 16 power set points based on any difference between the recipe and the real-time measurements. These power set points are sent to the drivers, which transmit appropriate voltages to the heating mechanism 44 and/or the heater(s) in the build area platform 16. This is one example of the heating system components 66, and it is to be understood that other heat control systems may be used. For example, the controller 62 may be configured to control the heating mechanism 44 and/or the heater(s) in the build area platform 16.

It is to be understood that the ranges provided herein include the stated range and any value or sub-range within the stated range. For example, from about 500° C. to about 3500° C. should be interpreted to include not only the explicitly recited limits of from about 500° C. to about 3500° C., but also to include individual values, such as about 690° C., 1000.5° C., 2055° C., 2750° C., etc., and sub-ranges, such as from about 900° C. to about 3250° C., from about 525° C. to about 2500° C., from about 1020° C. to about 2020° C., etc. Furthermore, when “about” is utilized to describe a value, this is meant to encompass minor variations (up to +/−10%) from the stated value.

Reference throughout the specification to “one example”, “another example”, “an example”, and so forth, means that a particular element (e.g., feature, structure, and/or characteristic) described in connection with the example is included in at least one example described herein, and may or may not be present in other examples. In addition, it is to be understood that the described elements for any example may be combined in any suitable manner in the various examples unless the context clearly dictates otherwise.

While several examples have been described in detail, it is to be understood that the disclosed examples may be modified. Therefore, the foregoing description is to be considered non-limiting. 

What is claimed is:
 1. A method for three-dimensional (3D) printing, comprising: patterning build material layers to form an intermediate structure, the patterning including: selectively applying a binding agent to define: a build material support structure and a patterned intermediate part; and selectively applying i) the binding agent and a separate agent including a gas precursor or ii) a combined agent including a binder and the gas precursor to define a patterned breakable connection between at least a portion of the build material support structure and at least a portion of the patterned intermediate part; and heating the intermediate structure to a temperature that activates the gas precursor to create gas pockets in the patterned breakable connection.
 2. The method as defined in claim 1 wherein the heating involves exposure to a series of temperatures that form: a 3D object from the patterned intermediate part; a 3D support structure from the build material support structure; and an irreversibly breakable connection from the patterned breakable connection, the irreversibly breakable connection including the gas pockets and being positioned between the 3D object and the 3D support structure.
 3. The method as defined in claim 2 wherein the heating involves: heating the intermediate structure to a de-binding temperature; and then heating the intermediate structure to an initial sintering temperature, followed by a gas pocket formation temperature, followed by a final sintering temperature.
 4. The method as defined in claim 2, further comprising removing the 3D support structure from the 3D object by breaking the irreversibly breakable connection.
 5. The method as defined in claim 1 wherein the patterned intermediate part at least partially overlies the build material support structure.
 6. The method as defined in claim 1 wherein patterning the build material layers includes: patterning a first build material layer by selectively applying the binding agent to define: a layer of the build material support structure and a layer of the patterned intermediate part separated by non-patterned build material; applying an other layer of build material on the patterned first build material layer; patterning the other layer of build material by: selectively applying i) the binding agent and the separate agent or ii) the combined agent on a portion of the other layer of build material that overlies the build material support structure, thereby forming the patterned breakable connection; and selectively applying the binding agent on an other portion of the other layer of build material to define an outer layer of a region of the patterned intermediate part; and forming a remaining region of the patterned intermediate part on the patterned breakable connection and in contact with the region of the patterned intermediate part, thereby forming the intermediate structure including the patterned intermediate part and the build material support structure temporarily bound together at the patterned breakable connection.
 7. The method as defined in claim 6 wherein the build material support structure is a multi-layer structure, and wherein prior to patterning the other layer of build material the method further comprises iteratively applying additional build material layers and selectively applying the binding agent to the additional build material layers to define several layers of the build material support structure and several layers of the region of the patterned intermediate part, wherein the several layers of the build material support structure and the several layers of the region of the patterned intermediate part are separated by additional non-patterned build material.
 8. The method as defined in claim 7 wherein the forming of the remaining region of the patterned intermediate part includes: applying a further layer of build material on the patterned breakable connection and the outer layer of the region of the patterned intermediate part; and selectively applying the binding agent to the further layer to define a patterned layer of the remaining region of the patterned intermediate part.
 9. The method as defined in claim 1 wherein patterning the build material layers includes: iteratively applying individual build material layers; selectively applying the binding agent to each of the individual build material layers to define several layers of the build material support structure and several layers of the patterned intermediate part; and selectively applying the i) the binding agent and the separate agent or ii) the combined agent on each of the individual build material layers to define the patterned breakable connection between the several layers of the build material support structure and the several layers of the patterned intermediate part.
 10. The method as defined in claim 1 wherein the gas precursor is selected from the group consisting of a transition metal hydride, an alkaline earth carbonate that releases carbon dioxide when activated, and a solid state mixture of an oxidizable species and an oxidizing agent to produce an oxidation product in a gas state at a sintering temperature used during the heating.
 11. The method as defined in claim 10 wherein one of: the gas precursor is the transition metal hydride, and the method further comprises exposing the intermediate structure to hydrogen gas during the heating; or the gas precursor is the solid state mixture, and the method further comprises exposing the intermediate structure to an inert gas or a vacuum environment during the heating.
 12. A liquid functional agent for three-dimensional (3D) printing, comprising: a compound that is to be activated at a temperature within a sintering temperature range of a build material of an intermediate structure to generate gas pockets within a portion of the intermediate structure that is patterned with the liquid functional agent, the compound being selected from the group consisting of a transition metal hydride, an alkaline earth carbonate selected from the group consisting of barium carbonate and strontium carbonate, and a solid state mixture of an oxidizable species and an oxidizing agent to produce an oxidation product in a gas state in the sintering temperature range; any of a surfactant or a dispersing aid; a co-solvent; and a balance of water.
 13. The liquid functional agent as defined in claim 12 wherein: the compound is the transition metal hydride, and the transition metal hydride is titanium hydride; or the compound is the solid state mixture and the oxidizable species includes carbon particles and the oxidizing agent is a transition metal oxide selected from the group consisting of Fe₂O₃, Mn₂O₃, Cr₂O₃, and Co₃O₄.
 14. The liquid functional agent as defined in claim 12, further comprising a binder.
 15. A three-dimensional (3D) printed article, comprising: a first object; a second object; and an irreversibly breakable connection between the first and second objects, wherein the irreversibly breakable connection comprises gas pockets. 